1. Technical Field
The present invention relates to a method of reducing emissions in the exhaust gases from an internal combustion engine. More specifically, the invention relates to a method of reducing exhaust gas emissions that includes supplying an air/fuel mixture to at least one cylinder when the engine crankshaft rotates, and controlling the opening and closing of one or more intake and exhaust valves based on the position of a piston in the cylinder.
2. Background Information
In internal combustion engines, it is desirable to reduce the undesirable emissions present in the exhaust gases of the internal combustion engine in order to reduce pollution of the surrounding environment and to satisfy legal requirements for internal combustion engines. The undesirable emissions present in the exhaust gases include, inter alia, carbon monoxide (xe2x80x9cCOxe2x80x9d), hydrocarbon compounds (xe2x80x9cHCxe2x80x9d) and nitrous oxides (xe2x80x9cNOXxe2x80x9d).
In order to reduce these exhaust gas emissions, the internal combustion engine is provided with a catalytic converter that completely, or nearly completely burns the emissions by means of a chemical reaction. This chemical reaction occurs only when the catalytic converter has reached a predetermined working temperature, which is reached after a predetermined operating time of the internal combustion engine. During cold-starts of the internal combustion engine, no reduction of the emissions occurs in the catalytic converter.
There are known arrangements for heating the catalytic converter when the internal combustion engine is cold-started. The intent of these arrangements is to rapidly reach a desirable working temperature of the catalytic converter in order to make it possible to reduce the exhaust gas emissions in the internal combustion engine at an early stage. In one such known arrangement, an electric heating element is arranged in the catalytic converter. However, this arrangement makes the catalytic converter complicated and expensive to produce.
Another problem that occurs when internal combustion engines are cold-started is that a comparatively great amount of fuel in relation to the air supplied, or a rich air/fuel mixture, has to be supplied to the internal combustion engine so that the internal combustion engine starts and is capable of working at a substantially constant speed when idling. This rich air/fuel mixture is also supplied so that the internal combustion engine is ready to provide increased torque when the accelerator is operated. By doing so, the drivability of the internal combustion engine is ensured before the internal combustion engine has reached its operating temperature. Without any emission control in the catalytic converter during this cold-start period, the rich air/fuel mixture results in the content of CO, HC and NOx emitted from the internal combustion engine being high when the engine is cold-started.
Previous attempts have been made to reduce the quantity of fuel in relation to the air supplied, i.e., run the internal combustion engine with a leaner air/fuel mixture when the internal combustion engine is cold-started. However, this results in the internal combustion engine working very unevenly when idling, as well as poor drivability of the internal combustion engine. The speed varies during idle running due to the torque generated by the internal combustion engine being very sensitive to variations in the lambda value of the air/fuel mixture supplied to the cylinder space of the internal combustion engine when the air/fuel mixture is lean. The lambda value, or excess air factor, is the actual air quantity supplied divided by the air quantity theoretically necessary for complete combustion. If the lambda value is greater than 1, the air/fuel mixture is lean. If the lambda value is less than one, the air/fuel mixture is rich.
The fuel supplied from a fuel injection valve can be accurately controlled by the fuel injection system of the internal combustion engine so as to obtain a substantially constant lambda value for the air/fuel mixture supplied. However, when the internal combustion engine is cold, fuel condenses on the comparatively cold walls in the intake duct and cylinder. The fuel condensed on the walls vaporizes during idling and accompanies the air/fuel mixture flowing in the intake duct and being supplied to the cylinder space. If vaporization of the fuel condensed on the walls is uneven, for example, due to pressure variations, temperature gradients, or flow rate of the air/fuel mixture in the intake duct, a variation in the lambda value of the air/fuel mixture supplied to the cylinder space occurs.
As torque generated by the internal combustion engine varies during idling when cold-started, the speed of the internal combustion engine varies. In this regard, the speed of the internal combustion engine refers to the speed of rotation of the crankshaft of the internal combustion engine. When the speed varies, the pressure in the intake duct will also vary. This, in turn, leads to the vaporization of the condensed fuel varying so that a variation of the lambda value of the air/fuel mixture supplied to the cylinder space occurs, resulting in the uneven speed of the internal combustion engine being intensified.
Accordingly, there is a need for controlling the amount of the air/fuel mixture supplied to the internal combustion engine during cold-starts so that the speed of the engine is made more even. Further, there is a need for controlling the internal combustion engine during cold-starts so that exhaust gas emissions are reduced.
The internal combustion engine of the present invention includes at least one cylinder to which an air/fuel mixture is supplied when the engine crankshaft rotates, at least one intake valve, at least one exhaust valve, control members for controlling the opening and closing of the intake and exhaust valves, and a piston reciprocating between a top dead-center position and a bottom dead-center position in the cylinder. The one or more exhaust valves are controlled so that they open before the piston passes the bottom dead-center position and close before the intake valve opens.
The present invention provides a method of reducing carbon monoxide (xe2x80x9cCOxe2x80x9d), hydrocarbon compounds (xe2x80x9cHCxe2x80x9d) and nitrogen oxides (xe2x80x9cNOxxe2x80x9d) in the exhaust gases from an internal combustion engine when cold-started. The invention also makes it possible for an internal combustion engine to run with a lean air/fuel mixture. The method of the present invention further provides a means of reaching the working temperature of the catalytic converter as rapidly as possible.
This is achieved according to the method of the present invention for reducing exhaust gas emissions that includes supplying an air/fuel mixture with a lambda value greater than 1 to the cylinder, and controlling the intake valve so that it opens during the intake stroke after the piston has passed the top dead-center position.
By supplying an air/fuel mixture greater than 1 to the cylinder, the emissions in the exhaust gases emitted from the internal combustion engine are reduced. The internal combustion engine will work at a substantially constant speed during idling by controlling the intake valve so that it opens after the piston has passed the top dead-center position, and by controlling the exhaust valve so that it closes before the intake valve opens. By doing so, exhaust gases are prevented from flowing into the intake duct. This results in even vaporization of the fuel condensed on the walls of the intake duct.
By opening the intake valve after the piston has passed the top dead-center position, powerful swirling or mixing of the air/fuel mixture supplied to the cylinder space is also obtained. By controlling the exhaust valve so that it opens before the piston has passed the bottom dead-center position, the expansion stroke of the piston in the cylinder is interrupted, allowing very hot exhaust gases to flow out through the exhaust duct and on to the catalytic converter, thereby rapidly heating the converter.